1. Field of the Invention
The present invention relates to an image display apparatus capable of displaying an image on a given plane of projection by beam raster scanning.
2. Description of the Background Art
Optical scanners deflecting and scanning light beams such as laser beams are utilized for optical equipment such as a barcode reader, a laser printer, and a display. Some such optical scanners include a polygon mirror scanning reflected light by rotation of a polygonal shaped mirror with a motor, a galvano-mirror causing a plane mirror to rotate and oscillate with an electromagnetic actuator, or the like. Such optical scanners require mechanical drive mechanisms for driving a mirror with a motor or with an electromagnetic actuator; however, such drive mechanisms are relatively large in size and expensive, inhibiting miniaturization of the optical scanners and increasing the cost thereof.
For miniaturization, cost reduction, and improved productivity of optical scanners, development of micro optical scanners where components such as mirrors and elastic beams are molded in one piece is now in progress using micromachining technologies for micromachining silicon or glass with application of semiconductor manufacturing technologies.
There is an image display apparatus which is provided with two such optical scanners as described above and displays a two-dimensional image on a plane of projection by raster scanning of light beams reflected off mirrors of those scanners.
This kind of image display apparatus suffers from a tapering phenomenon during raster scanning, which is so-called raster pinch, due to oscillatory drive of the mirrors in a horizontal scanning direction. The raster pinch is, however, vertical distortion of a displayed image and thus can be reduced by electrical correction of distortion in vertical scanning (see for example, Published Japanese Translation of PCT International Application No. 2003-513332).
In the image display apparatus described above, it is ideal that the trajectory of scanning lines describe a rectangle with a prescribed aspect ratio (cf. (b) in FIG. 12), but such a rectangle may in some cases be distorted (cf. (a) in FIG. 12) depending on the properties of optical devices employed, the angle of the plane of projection relative to light beams, or the like. One technique for correcting such distortion in raster scanning in a horizontal scanning direction (main scanning direction) is, for example, a distortion correction technique using optical devices with optical properties of canceling distortion.
However, this distortion correction technique needs installation of the optical devices described above, complicating the configuration and causing an increase in the size and cost of the image display apparatus as a whole.